Hopefully the cisco copper GBIC supports Auto-MDI though, so a straight cable should be good.
S
Hi,
I've had a lot of emails asking me how I was getting on with this, so I figured I'd do a quick redux of the issues for the archives.
One of the main problem actually turned out to be a damaged strand in the CAT5e underfloor cabling, which meant that the connection would work at 10/100, but not at 1000 (GE) because of the use of extra pairs on GE. So leaving comments about castrating the cabling the engineer who assured me it had tested fine aside 
the other problems we encountered were:
Foundry's GE auto-negotiation seems very tempermental.
Another engineer here just told there's a connection (on SX/MM) between a Foundry BigIron and clients Dell switch in the network where both ends only get a link light when the Foundry is configured to neg-full-auto (Autonegotiation first, if failed try non-autonegotiation). auto-gig (Autonegotiation) and neg-off (Non-autonegotiation) don't work! Only neg-full-auto on which the connection is fine and stable.
We ditched the copper GBIC and used a 1000Base-SX to 1000Base-TX convertor. The foundry won't form a real link (from a fixed SX/SC blade) with the 1000Base-SX convertor until "gig-default auto-gig" is entered. With the default settings both ends get a link light but the Foundry never sees any mac-addresses.
The cisco 2950T does support auto MDI/MDI-X on the gigabit copper ports dispite this not being mentioned in the any switch specification I could find. I never did have any luck with a GE cross-over cable (even not using the damaged underfloor cabling).
Dispite never being able to get a link-light between the Foundry Copper GBIC and the cisco 2950T, I've since found another point in our network, using exactly the same model GBIC in this configuration, that's working fine. The GBIC has since been placed back into a cisco 6500 where it's working fine (hooked at to a 10/100/1000 port on another cisco 6500).
So, multi-vendor Copper GE - not always as easy as it sounds!
Sam